1. Field of the Invention
This invention relates an idling speed controlling system for an internal combustion engine.
2. Description of the Prior Art
Generally it is preferred to maintain the idling speed of the internal combustion engine of a vehicle at a low speed of about 600 to 700 rpm from the viewpoint of fuel consumption and stability of the combustion in the engine. In unexamined Japanese Utility Model Publication 55(1980)-137234 is disclosed a feedback control system for controlling the idling speed of an engine in which the throttle valve is opened and closed under control so as to maintain the idling speed constant.
This prior art system carries out the feedback control when it is detected that the throttle valve is in the idling position. However, the throttle valve may be in idling position even when the engine is operating at high rotational speed as in a case where the braking effort of the engine is being used to slow the vehicle and at these times it is not preferred to carry out feedback control as if the engine were actually idling. Thus, there has been proposed a feedback control system for controlling the idling speed in which the actual idling speed is compared with a desired idling speed determined according to the operating conditions of the engine, and a control valve for controlling the amount of air to be fed to the engine is adjusted to equalize the actual idling speed to the desired idling speed according to the result of the comparison. In this system, the engine is considered to be idling when the actual opening angle of the throttle valve is smaller than a predetermined value and at the same time the actual rotational speed of the engine is lower than a predetermined value, and the feedback control is carried out to equalize the actual rotational speed to said desired idling speed. This system is disadvantageous in that if the predetermined value of the rotational speed below which the engine is considered to be idling (this value will be referred to as the "reference idling speed" hereinbelow) is set at a low value, there is the possibility of engine's stalling due to delay in the control system since the control system does not operate until the rotational speed of the engine is substantially lowered, while if the reference idling speed is set at a high value, the braking effect of the engine brake will be reduced since the engine is considered to be idling and the control valve is opened while the vehicle is still running due to premature operation of the control system.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide an improved idling controlling system for an internal combustion engine in which the idling speed of the engine is effectively controlled without causing stalling of the engine even if the rotational speed of the engine is abruptly lowered as is often the case after racing, and at the same time without reducing the braking effect of the engine.
In accordance with the present invention, the actual rotational speed of the engine and the actual opening angle of the throttle valve are detected, and at the same time it is detected whether or not the driving power of the engine is transmitted to the driving wheels. When the opening angle of the throttle valve becomes smaller than a predetermined value and at the same time the rotational speed of the engine becomes lower than the reference idling speed set at a higher value when the driving power is not transferred to the driving wheels than when the driving power is transmitted to the same, control is carried out to equalize the actual idling speed to a desired idling speed determined according to the operating conditions of the engine.
Thus in the idling controlling system of the present invention, when the driving power is not transmitted to the driving wheels and there is the possibility of the engine's stalling if the rotational speed thereof should be abruptly lowered, the control is carried out before the rotational speed is lowered to such extent as to cause stalling of the engine, whereby stalling of the engine can be effectively prevented, while when the driving power is transferred to the driving wheels and there is hardly any possibility of the engine's stalling, the control is not carried out until the rotational speed of the engine is sufficiently lowered, whereby reduction of the braking effect of the engine due to premature operation of the system is prevented.
The present invention can be carried out either in the form of a system in which the idling speed of the engine is controlled by controlling the throttle valve itself or in the form of a system in which the idling speed is controlled by controlling a bypass valve for adjusting the amount of air to be fed to the engine through a bypass passage which bypasses the throttle valve.